The NAND type flash memory is applied to a file memory and a mobile memory, and recently the NAND type flash memory is just beginning to be applied as a replacement for an HDD of a notebook personal computer (as an SSD: solid state drive). As used herein, “file memory” means the NAND type flash memory that is solely incorporated in a memory card, a USB, a digital device, and the like, and “mobile memory” means the NAND type flash memory such as an MCP (multi chip package) incorporated in a cellular phone, which is used by combining plural kinds of memories (such as a NOR type flash memory).
Under these circumstances, there is a need to increase a memory capacity in the NAND type flash memory. Therefore, it is necessary to develop a product of 128 gigabits or more as the memory capacity of one chip.
However, when memory cells are fabricated more finely to increase the memory capacity, word lines disposed on a memory cell array become thinned and lengthened. As a result, chip performance (such as write/erase/read rate) degrades.
A floor plan in which a row decoder is disposed at one end or both ends of the memory cell array is adopted in the conventional NAND type flash memory.
In order to prevent the degradation of the chip performance in the floor plan, it is necessary that one memory cell array be divided into plural memory planes (memory plane) to shorten the word line.
However, the number of row decoders increases as the number of memory planes increases, which results in a problem in that a chip area enlarges.